1. Field of the Invention
This invention relates to a clear, thixotropic, water based general purpose, polyvinyl alcohol adhesive gel for porous and semiporous substrates such as paper, card board, cloth and wood.
2. Background Art
Many different general purpose adhesives are available for adhering porous and semiporous substrates such as paper. However, such adhesives have shortcomings for use in projects which are performed on wall boards and other vertical surfaces such as in a class room by young children.
The adhesive gels of this invention consist essentially of: water; a partially hydrolyzed polyvinyl alcohol: a water-soluble thickening agent polymer which is compatible with polyvinyl alcohol; a water-soluble defoamer; and a water-soluble plasticizer for the polyvinyl alcohol which does not destroy the clarity of the gel. Optionally, other ingredients can be added which do not destroy the advantageous properties of the gel. Compatible preservatives are generally added to the gel.
The Handbook of Water-Soluble Gums and Resins by R. L. Davidson, 1980 by Mc Graw-Hill, Inc. pages 20-20 discloses partially hydrolyzed polyvinyl alcohol as an adhesive and page 20-18 discloses the use of certain gelling agents to control penetration of polyvinyl alcohol solutions into porous substrates or to prevent run-off of coating by dipping whereas page 20-19 of that reference discloses the use of an antifoam agent with polyvinyl alcohol. Pages 21-15 and 21-16 of the Handbook reference describe adhesive properties of polyvinylpyrrolidone (PVP). Among other shortcomings, these references do not mention the use of thixotropic agents with polyvinyl alcohol nor proportions of ingredients used in obtaining the advantageous properties of this invention.
U.S. Pat. No. 3,442,845 of May 6, 1969 to P. Columbus et al. relates to polyvinyl acetate adhesives which are redispersible in cold or hot water. The adhesive compositions of the 845 patent use polyvinyl alcohol, water-soluble gums, and cellulose ethers as anti-coalescing agents for the polyvinyl acetate. Propylene glycol and other polyhydroxy compounds are mentioned as plasticizers for polyvinyl alcohol. However, among other shortcomings in relation to the adhesive gel of this invention, the adhesive of the 845 patent does not have the thixotropic properties, clarity, or rate of set of the adhesive gel of this invention.
U.S Pat. No. 4,251,400 of Feb. 17, 1981 to P. Columbus also relates to a polyvinyl acetate adhesive which is redispersible in hot and cold water in the dried film form and which uses polyvinylpyrrolidone and a non-volatile, water-soluble, plasticizer as the anti-coalescing agent. In addition to the polyvinyl acetate and polyvinylpyrrolidone that patent also mentions the use of polyvinyl alcohol, propylene glycol, as well as water-soluble ethers in the adhesive composition. The adhesive of the 400 patent lacks many of the properties of the adhesive gel of this invention such as rate of set, clarity, and the thixotropic properties.
A mucilage containing about 83% of water; 14% of partially hydrolyzed polyvinyl alcohol; 0.2% of a water-soluble polyalkoxylated polyether defoamer; 1.8% of propylene glycol and a total of about 0.25% of boric acid and citric acid as thickeners is a well known commercial product. Again, this mucilage lacks properties of the adhesive gel of this invention such as the thixotropy and wet tack.
European Patent Application Publication Number 0210052 to Locktite which was published on Jan. 28, 1987 relates to various tubes for dispensing reactive adhesives such as cyanoacrylate at a rate of one or two drops at a time. The patent mentions resilient plastic tube dispensers and broadly states that the adhesive can be thixotropic.